There can be multiple reasons for this…
1. the B-paper was peeled too cold, meaning the glue ripped the toner off the A-foil
–> to avoid this issue make sure to peel the B-paper while it’s still warm/hot and make sure you don’t lift the A-Foil up or remove it from the heat press.
2. the the papers were placed in the wrong order, thus the pressure is not distributed the “right-way”.and instead of the glue getting applied on the toner the toner gets applied onto the glue
–> to avoid this always place the B-paper on top of the A-Foil and not the other way around.
3. the pressure of the heat press is set too high and thus the glues “sticks” too much
–> make sure your pressure is only set to medium pressure (=2-3 bar = 30-43 psi)
hope this helps!